The invention relates to an applicator pen for liquids.
The applicator pen for liquids contains an applicator element in the shape of a brush or wick which, in the position of rest, is retracted into the bore of a nozzle and which can be brought into the position of use against the force of a pressure spring by means of an actuating element. In the course of operation the applicator element is wetted with liquid from the reservoir in a metered manner. At the end of its use or after release of the activation element, the applicator element is returned into the initial position, where the applicator element is protected from quick drying out and damage.
A pen-like device is known from German Letters Patent DE-PS 36 29 627 which, similar to the present invention, supplies a brush-like applicator element with liquid in a metered manner when the brush has been brought into the position of use by means of an activation element.
However, the structure of the metering system and its function differ from those of the invention.
In the prior art design the metering operation is the result of the cooperation between a control piston, fixedly connected with the piston rod, and a resiliently attached metering piston which is axially movable on the piston rod. After the control piston has left its associated seal at the start of its longitudinal movement, the control piston, which is pre-stressed by a metering spring, is in a position to move into the sealing cylinder and to displace the liquid.
The resilient connection by means of the metering spring has the disadvantage that metering, i.e. the movement of the metering piston, depends on the friction of the metering piston in the sealing cylinder. With increased friction the metering piston initially remains stationary during operation until the metering spring has achieved pre-stressing which overcomes the static friction of the metering piston. This pre-stress build-up has the result that the metering piston is suddenly placed into sliding friction. Because of this the metered amount present in the metering chamber is displaced suddenly and uncontrolled out of the metering chamber.
The liquid leaves the nozzle in an undesirable manner. Because of this, even wetting of the applicator element does not take place and useful application is not possible.
Just as disadvantageous a result is created if in the known design the friction between metering piston and piston rod is too great. In this case the metering piston is taken along at the speed of actuation, so that in case of rapid actuation a metering pulse takes place which also results in an uncontrolled expulsion of liquid particles.
It is furthermore disadvantageous that operation becomes stiff because of increased friction between the metering piston and the piston rod and that the return spring is no longer able to return the piston rod with the metering piston into the initial position. Because of this the metering piston remains in the sealing cylinder, so that the metering chamber cannot be filled for the following metering step and application becomes impossible.
A further disadvantage of the prior art in comparison with the invention, is the need to produce an increased amount of parts having very close tolerances to achieve useful application.